1. Technical Field
The present invention, involving Group-III nitride crystal and methods of its manufacture, relates to epitaxial III-nitride crystal in composites in which the epitaxial crystal has a major surface of plane orientation other than {0001}, designated by choice, and other special properties.
2. Description of the Related Art
Group-III nitride crystals, which are employed advantageously in semiconductor electronic devices including light-emitting devices and semiconductor sensors, are ordinarily manufactured by growing crystal onto the major surface of a sapphire substrate having a (0001) plane major surface, or onto a GaAs substrate having a (111) A-plane major surface, by means of a vapor-phase technique such as hydride vapor-phase epitaxy (HVPE) or metalorganic chemical vapor deposition (MOCVD), or by flux growth or other liquid-phase technique. Consequently, ordinarily obtained III-nitride crystals have a major surface whose plane orientation is {0001}.
With light-emitting devices on substrates that are III-nitride crystal having a major surface whose plane orientation is {0001}, and in which a multiquantum-well (MQW) structure as a light-emitting layer has been deposited on the major surface, the light-emission efficiency is decreased by spontaneous polarization that occurs within the light-emitting layer owing to the III-nitride crystal's <0001> oriented polarity. Consequently, the manufacture of III-nitride crystal having a major surface whose plane orientation is other than {0001} is being sought.
Reference is made, for example, to Japanese Unexamined Pat. App. Pub. No. 2005-162526: The following method has been proposed as way of preparing gallium-nitride crystal having a surface plane orientation of choice, without influencing the plane orientation of the major surface of the substrate. Namely, according to the method disclosed in Pat. App. Pub. No. 2005-162526, a number of rectangular crystal masses are diced from GaN crystal grown by vapor deposition. Meanwhile, a silicon oxide film is coated onto the surface of a separately readied sapphire substrate, and subsequently a number of recesses reaching to the substrate are formed in the film. Next, the numerous crystal masses are embedded into the recesses in a manner such that their top surfaces will have the same plane orientation. Then, by vapor deposition with the crystal masses as seeds, gallium nitride crystal having a surface plane orientation of choice is grown.